1. Field of the Invention
This invention relates to a transverse direction electric field system active matrix liquid crystal display device. More particularly, this invention relates to a technology that will reduce the defect called xe2x80x9cweighting tracexe2x80x9d that develops when a weight or a load is applied to the display surface, and that can be recognized for a long time even after the removal of weighting.
2. Description of the Related Art
In an active matrix liquid crystal display device described in Japanese Patent Laid-Open No. Hei 8-254712, for example, a transverse electric field system that sets the direction of the electric field applied to a liquid crystal to a direction in parallel with substrates has been used mainly as means for acquiring a ultra-wide visual field angle. It has been clarified that this system substantially eliminates the change of contrast and inversion of a gradation level when the visual field angle is changed (refer to M. Oh-e et al. xe2x80x9cAsia Displayxe2x80x9d, 1995, pp.577-580).
FIG. 10 of the accompanying drawings is a plan view showing a pixel portion of an ordinary transverse direction electric field system liquid crystal display device according to the prior art. In the drawing, reference numeral 2 denotes a gate wire as a plurality of scanning signal lines formed on an insulating substrate. The gate wire 2 crosses a source wire 12 as a plurality of video signal lines. Reference numeral 4 denotes a holding capacitance common wire. Reference numeral 6 denotes a semiconductor film of a thin film transistor disposed at each point of intersection between the gate wire 2 and the source wire 12. Reference numeral 9 denotes a holding capacitance electrode disposed over the holding capacitance common wire 4 through a gate insulating film. Reference numeral 10 denotes a comb-like pixel electrode comprising a plurality of electrodes each connected to the thin film transistor and that are disposed in parallel with the source wire 12. Reference numeral 11 denotes a comb-like opposed electrode comprising a plurality of electrodes that are disposed alternately and in parallel with a plurality of electrodes of the pixel electrode 10. Reference numeral 14 denotes a drain electrode and reference numeral 16 denotes a contact hole.
Such a transverse direction electric field system liquid crystal display device involves the problem of a so-called xe2x80x9cweighting tracexe2x80x9d. Namely, when a weight or a load is applied to the display surface, a display defect occurs round the weighted portion due to an abnormal orientation of the liquid crystal, and this display defect can be recognized for a long time even after the removal of the weight or the load. The principle of the occurrence of the weighting trace will be explained with reference to FIGS. 11 to 14. In FIGS. 11 to 14, the angle xcex81 is a angle between the direction Ds of source line and the orientation direction D1 of the liquid crystal. FIG. 11 shows the state where no voltage is applied to the liquid crystal and FIG. 12 shows the state where a voltage is applied to the liquid crystal. FIG. 13 shows the state where a voltage is applied to the liquid crystal and moreover, weighting is applied, too, and FIG. 14 shows the orientation of the liquid crystal molecules when the voltage is applied to the liquid crystal and after weighting is removed. When the voltage is not applied to the liquid crystal, the liquid crystal molecules are aligned in the orientation direction determined by the liquid crystal orientation method such as rubbing as shown in FIG. 11. When the voltage is applied to the liquid crystal, the liquid crystal molecules are oriented in the direction of the electric field. At this time, the direction of the electric field changes at the end portions of the pixel electrode 10 and at the end portions of the counter electrode 11 as shown in FIG. 12. Inconsequence, regions develop in which the liquid crystal rotates in the reverse direction, inviting orientation defect regions 22 at the boundaries with the regions in which the liquid crystal rotates in the normal direction. This orientation defect region occurs only in the proximity of the electrode end portions under the voltage application state and the steady state, and can hardly be recognized, in consequence. When weighting is applied to the display surface under the voltage application state, however, the orientation defect region 22 at each end portion of the pixel electrode 10 and the orientation defect region 22 at each end portion of the counter electrode 11 expand as shown in FIG. 13, and these orientation defect regions 22 can be recognized. Majority of these orientation defect regions 22 return to the initial state after weighting is removed, but a part of them remains for a long time, can be recognized and remarkably lowers display quality as shown in FIG. 14.
FIGS. 11 to 14 illustrate the case where the orientation direction of the liquid crystal is counter-clockwise to the source wire 12. FIGS. 15 to 17 show the case where the orientation direction of the liquid crystal is clockwise to the source wire 12. In FIGS. 15 to 17, the angle xcex81xe2x80x2 is a angle between the direction Ds of source line and the orientation direction D2 of the liquid crystal in this case. FIG. 15 shows the state where the voltage is applied to the liquid crystal. FIG. 16 shows the state where the voltage is applied to the liquid crystal and moreover, weighting is applied, too. FIG. 17 shows the orientation of the liquid crystal molecules under the state where the voltage is applied to the liquid crystal and weighting is removed. In this way, the occurring positions of the abnormal orientation regions 22 in the case where the orientation direction of the liquid crystal is clockwise with respect to the source wire 12 have symmetry of line with the occurring position of the abnormal orientation regions 22 when the orientation direction of the liquid crystal is counter-clockwise, and with respect to the source line 12.
Means that increases the rubbing angle is generally known as a method of reducing the weighting trace described above. In the transverse direction electric field system, however, the visual field angle direction in which the contrast is high is the rubbing angle direction, that is, the orientation direction of the liquid crystal, and the direction orthogonal to the former. Therefore, the problem arises afresh that when the rubbing angle is increased, the visual field angle characteristics of the display device in vertical and transverse directions drop. Because a driving voltage becomes greater with the increase of the rubbing angle, another problem develops further in that low voltage driving becomes difficult.
To solve the problems described above, the present invention is directed to provide a transverse direction electric field system liquid crystal display device that can reduce the display defect called xe2x80x9cweighting tracexe2x80x9d, in which a display defect occurring due to weighting to the display surface is recognized for a long time even after the removal of weighting, has a wide visual field angle and excellent display characteristics, and can be produced easily and economically.
According to one aspect of the present invention, there is provided a liquid crystal display device including a pair of substrates so disposed in the spaced-apart relation as to oppose each other with a predetermined distance between them; a liquid crystal layer sandwiched between the substrates; a plurality of scanning signal lines and a plurality of video signal lines so formed on one of the substrates as to cross one another; thin film transistors each being disposed at the point of intersection between the scanning signal line and the video signal line; a comb-like pixel electrode comprising a plurality of electrodes each connected to the thin film transistor and disposed in parallel with the video signal line; and a comb-like counter electrode comprising a plurality of electrodes disposed alternately and in parallel with a plurality of electrodes of the pixel electrode; the liquid crystal display device applying a voltage between the pixel electrode and the counter electrode to thereby apply an electric field substantially in parallel with the substrate surface to the liquid crystal layer, wherein: a bent portion bent in a direction opposite to an orientation direction of the liquid crystal with respect to the video signal line is disposed at the distal end portion of at least one of the pixel electrode and the counter electrode.
The bent portion is disposed at the distal end portion of the comb-like pixel electrode.
The opposed electrode has a projection portion protruding in the same direction and at the same angle as the bent portion at a position thereof adjacent to the bent portion formed at the distal end portion of the pixel electrode.
Recess portions of a plurality of comb-like electrodes of the counter electrode are bent in parallel with the bent portions formed at the distal end portions of the adjacent pixel electrodes.
The bent portion is formed at the distal end portion of each comb-like counter electrode.
The pixel electrode has a projection portion protruding in the same direction and at the same angle as the bent portion at a position thereof adjacent to the bent portion formed at the distal end portion of the counter electrode.
Recess portions of a plurality of comb-like electrodes of the pixel electrode are bent in parallel with the bent portions formed at the distal end portions of the adjacent counter electrodes.
According to another aspect of the present invention, there is provided a liquid crystal display device including a pair of substrates so disposed in the spaced-apart relation as to oppose each other with a predetermined distance between them; a liquid crystal layer sandwiched between the substrates; a plurality of scanning signal lines and a plurality of video signal lines so formed on one of the substrates as to cross one another; thin film transistors each being disposed at the point of intersection between the scanning signal line and the video signal line; a comb-like pixel electrode comprising a plurality of electrodes connected to the thin film transistors and disposed in parallel with the video signal line; a comb-like counter electrode comprising a plurality of electrodes disposed alternately and in parallel with a plurality of electrodes of the pixel electrode; the liquid crystal display device applying a voltage between the pixel electrode and the counter electrode to thereby apply an electric field substantially in parallel with the substrate surface to the liquid crystal layer, wherein: conductors having a pattern shape such that at least one of the sides thereof is inclined in a direction opposite to an orientation direction of the liquid crystal with respect to the video signal line are disposed at the distal end portions of at least one of the pixel electrode and the counter electrode, through an insulating film.
The conductors are electrically connected to the pixel electrode or the counter electrode through a contact hole.
The conductor comprises a conductor film having light transmissibility.